Design and Control of A Tilt-Rotor Tailsitter Aircraft with Pivoting VTOL Capability

TL;DR

The paper tackles actuator-saturation and limited roll control in tailsitter VTOL aircraft by proposing a TRE-tailsitter that combines dual tilt rotors with elevons. A cascaded weighted least squares INDI controller governs attitude and guidance, and a dedicated pivot takeoff/landing strategy enables stable VTOL from a level ground pose. Wind tunnel experiments and outdoor flight tests demonstrate improved roll control over tilt-rotor only designs and superior performance during vertical descent and transitions compared to elevon-only tailsitters, while achieving autonomous waypoint tracking at 16 m/s. Overall, the TRE-tailsitter delivers robust full-envelope performance with pivoting VTOL capability, suitable for autonomous operations and potentially high-speed drone racing.

Abstract

Tailsitter aircraft attract considerable interest due to their capabilities of both agile hover and high speed forward flight. However, traditional tailsitters that use aerodynamic control surfaces face the challenge of limited control effectiveness and associated actuator saturation during vertical flight and transitions. Conversely, tailsitters relying solely on tilting rotors have the drawback of insufficient roll control authority in forward flight. This paper proposes a tilt-rotor tailsitter aircraft with both elevons and tilting rotors as a promising solution. By implementing a cascaded weighted least squares (WLS) based incremental nonlinear dynamic inversion (INDI) controller, the drone successfully achieved autonomous waypoint tracking in outdoor experiments at a cruise airspeed of 16 m/s, including transitions between forward flight and hover without actuator saturation. Wind tunnel experiments confirm improved roll control compared to tilt-rotor-only configurations, while comparative outdoor flight tests highlight the vehicle's superior control over elevon-only designs during critical phases such as vertical descent and transitions. Finally, we also show that the tilt-rotors allow for an autonomous takeoff and landing with a unique pivoting capability that demonstrates stability and robustness under wind disturbances.

Figures (14)

• Figure 1: (Top) TRE-tailsitter executing a pivot takeoff, where it pitches up steadily off the ground by pivoting around its tail by thrust vectoring. (Bottom) Transition from hover to forward flight, captured at 0.1-second intervals.
• Figure 2: The top view of the TRE-tailsitter.
• Figure 3: Tilt rotor configuration with positive rotor tilt and elevon deflection defined.
• Figure 4: The front and side views for the wind tunnel test setup, where the aircraft faces against a wind airflow of 15 m/s, representing the forward flight phase.
• Figure 5: Pitch and roll moments generated by either elevon deflection or rotor tilt at $15$ m/s airspeed, with only one side rotor tilted or elevon deflected, under the assumption that the left and right actuators have symmetrical effects.